Among the volatile chlorinated hydrocarbons, the chloroethenes (common name: chloroethylenes) such as tetrachloroethene (PCE) and trichloroethene (TCE), are major environmental contaminants which cause soils and ground water contamination. There are biological, chemical and physical means to treat soil and ground water contaminated chloroethenes. In the biological methods, microbial activities are used to degrade the contaminants. Chemical oxidants are used to degrade contaminants in chemical method. In physical approach, contaminated soils or ground water is removed or replaced. Among them, a biological method, in situ bioremediation, using anaerobic processes by supplying hydrogen-releasing compounds is thought to be the most promising means of cleaning up soils or groundwater contaminated with chloroethenes.
The biological method utilizes dehalorespiration performed in some microbes including Dehalococcoides species that uses chlorinated organic compounds as electron acceptors under anaerobic conditions. In this method, PCE and TCE are reductively dechlorinated via the less chlorinated ethenes, cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC) to harmless ethene.
Dehalococcoides and Desulfitobacterium species are known as the microbes that are used for bioremediation of soils or ground water contaminated by chloroethenes. The previous studies on them are summarized as follows. Non-patent document 1 is the report on isolation of Dehalococcoides ethenogenes 195 that performs complete dechlorination of PCE to ethene. Non-patent document 2 describes that Dehalococcoides sp. BAV1 was isolated as the first anaerobic bacterium that dechlorinates VC and DCE to ethene. Non-patent documents 3 and 4 describe isolation of Dehalococcoides sp. VS that dechlorinates cis-1,2 DCE and VC to ethene and isolation of Dehalococcoides sp. FL2 that dechlorinates TCE and DCE to VC, respectively. In non-patent document 5, isolation and characterization of Dehalococcoides sp. GT that dechlorinates TCE through cis-1.2 DCE and VC to ethene are described.
As Desulfitobacterium strains, Desulfitobacterium dehalogenance, was reported in non-patent document 6. Patent document 1 and 2 refer to Desulfitobacterium strains that dechlorinate PCE, such as Desulfitobacterium sp. Y51 and Desulfitobacterium sp. KBC1.
According to reductive dehalogenases that are responsible for dechlorination of chloroethene, there are following documents: Patent documents 3 and 4 refer to PCE reductive dehalogenase (PCE). Non-patent document 7 refers to TCE reductive dehalogenase (TceA), and non-patent documents 8 and 9 refer to two VC reductive dehalogenases (BvcA and VcrA).
Patent document 5 describes methods for identification and quantification of reductive dehalogenase genes in the sample obtained from the sites contaminated by chloroethenes. Preparation of microbes for bioaugmentation is described in patent document 6.